There are hereby exempted from the provisions of this chapter and the computation of the tax imposed by it, the gross receipts received by a direct mail service for the cost of United States postage paid by the direct mail service if the cost of postage, including any markup that is reasonable and customary in the seller's industry, is listed by the direct mail service as a separate line item on the customer's bill.
For the purposes of this section, a direct mail service is any business that prepares direct mail.